Process for producing absorbent core structures

ABSTRACT

The present invention is method for forming a sandwich structure having a pattern of particulate material enveloped between a carrier material and a cover material. The method allows accurate forming of pre-determined pattern at high production speed. Such a method is particularly useful in the manufacture of disposable absorbent articles, such as baby diapers.

FIELD OF THE INVENTION

The present invention is a process for forming a sandwich structurehaving a pattern of particulate material enveloped between a carrier anda cover material. In a particular embodiment, the particulate materialis super absorbent material, and the sandwich structure is a liquidabsorbent structure for use in disposable absorbent products.

BACKGROUND

Composite structures comprising particulate material in a particularpattern are well known in the art, see, e.g. EP-1447066 (Busam et al.;P&G), disclosing an absorbent core for an absorbent article, which has aparticulate absorbent material that is immobilized when wet. Theabsorbent core comprises a substrate layer with an absorbent material,such as an absorbent polymer material.

U.S. Pat. No. 4,381,783 (Elias) discloses an absorbent article with acore comprising pockets of absorbent hydrocolloid material. Thesepockets are provided to confine the movement of absorbent polymermaterial, in particular when the article is fully or partially loadedwith urine. The pockets form part of an absorbent layer and aretypically provided from cellulose material. Hence, as to achieve goodimmobilization of the absorbent polymer material according to theteaching of this patent relatively high amount of cellulosic material isrequired. Moreover, the provision of such pockets may hinder the freedistribution of liquid to the more absorbent areas of the core, forexample the areas of the absorbent polymer materials.

Accordingly, processes to produce absorbent article having anon-homogeneous distribution of absorbent materials such as particulateabsorbent polymer material, often referred to as absorbent gellingmaterial or as superabsorbent, are also well known. In WO 03/101622A2(Tombuilt et al.; P&G) a pulsing process for creating discontinuousparticulate distribution is disclosed, and a similar structure may beproduced according to U.S. Pat. No. 5,213,817 (Pelley; McNeill PPC).

Processes aiming at depositing a pattern of particulate absorbentmaterial onto a web are described in U.S. Pat. No. 4,800,102 (Takada;Nordson), employing a rotating mask, or in WO 92/019198A(Perneborn/Mølnlycke) showing a linearly moving mask. FR-A-2583377(Piron; Colgate Palmolive) discloses a metering drum into whichabsorbent powder is fed from a hopper for creating discontinuous patternon a carrier on a conveyor belt. The drum is operated in a step-wisemovement.

U.S. Pat. No. 5,494,622 (Heath et al.; K-C), aims at producing pocketsof particles in a desired pattern on a web moving at high speed. Apattern chamber is supplied with particles of high absorbency materialthrough which a gas permeable web is transported on a surface having apattern of openings through which a vacuum is drawn so as to cause theparticles to be deposited on the web in the pattern of the openings inthe surface. The web carrying the particles is covered by a layer ofliquid permeable material or the tension applied to the permeable web isvaried to vary the porosity of the web. The particles are held on theweb in the desired pattern of pockets while surplus particles betweenthe pockets are removed. The thusly formed pockets form “islands”, i.e.they are completely surrounded by bonded regions.

Whilst such documents describe various approaches to the deposition ofparticulate material onto a surface or on a moving substrate, there isstill the need for a method to produce patterned particulate sandwichesin a very well defined pattern and at high production speeds.

SUMMARY

The present invention is a process of creating a sandwich structurecomprising particulate material sandwiched between web materials in avery well defined pattern. The method comprises the step of providing anessentially flat carrier material and an essentially flat cover materialfor forming the outer sandwich layers, which may be unitary for formingboth outer sandwich layers, or which may be different materials formingthe outer sandwich layers. Further steps provide an essentially endlesssupport means for the carrier material having a support pattern and acarrier material holding means. The carrier material is positioned overthe support means at a carrier speed relative to a fixed frame, wherebythe carrier means contacts the support pattern with its support surfaceand whereby the relative speed between carrier material and the contactsurface of the carrier support means is essentially zero. A particulatematerial is provided and pre-metered. The cover material and the carriermaterial are combined and affixed by a fixation means with theparticulate material positioned there between. The carrier material issupported only in the region of the support pattern of the support meansand deformed by a carrier holding means such that indentations areformed in the unsupported regions. The particulate material istransferred to the carrier material into the indentations; therebyforming a primary pattern of particulate material.

In preferred executions, the carrier material is a non-woven material,preferably of the SMS or SMMS type, and it may have a CD-extensibilityor a MD-extensibility of more the 20%, preferably more than 100%, buteven more preferably not more than 200%. The ratio of MD-extensibilityto the CD-extensibility is at a given load not more than one to two.Also the cover material can be a non-woven material, optionally beingthe same material as the carrier material.

The particulate material can be a bulk material, preferably asuperabsorbent, more preferably a partially cross-linked polyacrylatematerial.

In a preferred execution, the carrier support means is a rotatable drum,preferably having an outer cylinder shell. It is further preferred, thatthe carrier holdings means is a vacuum air suction.

The carrier support pattern may comprise support pins, which may have adistance of more than 5 mm and not more than 30 mm from each neighboringsupport pins. The support pins preferably have an outwardly extendingsurface of at least 0.8 mm², preferably of at least 4 mm², but not morethan 170 mm², preferably not more than 80 mm².

The sandwich fixation means is preferably thermo-bonding orglue-bonding, more preferably a sprayed adhesive. The bonding region isat least 2%, preferably at least 7%, but more preferably not more than50% of the area of the pattern area. Preferably, the bonding regioncomprises essentially no particulate material, as assessed by the methodfor determining the absence of particles in the bonding area.

The carrier holding means extends the carrier material such that itdeforms out of the original flat state forming an indentation.Preferably, the indentations have a volume of more than 30 mm³,preferably more than 100 mm³, but less than about 1000 mm³. Preferably,the particulate material fills more than 5% of the volume of theindentations, preferably not more than 150% of the volume of theindentations.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a top plan view of a disposable diaper, with the upper layerspartially cut away.

FIG. 2 shows a cross-sectional view of the disposable diaper of FIG. 1.

FIG. 3A shows a top view of an absorbent core sandwich structure.

FIG. 3B is a cross-sectional view of the sandwich pattern of FIG. 3A.

FIG. 4A is a schematic process diagram for forming a sandwich structure.

FIG. 4B is a schematic enlarged sectional view of a part of theequipment for the process as shown in FIG. 4A.

FIG. 5A is a schematic perspective presentation of the shell of acarrier support means.

FIG. 5B is a schematic cross-sectional view of the shell of FIG. 5A.

FIG. 5C is a schematic top view of a part of the shell of FIGS. 5A andB.

FIGS. 6A, C, E, and G show various embodiments of a carrier supportmeans, and FIG. 6B, D, F, H corresponding cross-sectional views.

DETAILED DESCRIPTION

The present invention aims at producing a patterned sandwich structure,which contains particulate material being sandwiched between a carriermaterial in a very well defined amount and pattern. Such structures areparticularly useful for disposable absorbent articles. Such articleshave very varying requirements as to the desired absorbency depending onthe intended use.

As used herein, the following terms have the following meanings:

“Absorbent article” refers to devices that absorb and contain liquid,and more specifically, refers to devices that are placed against or inproximity to the body of the wearer to absorb and contain the variousexudates discharged from the body. Absorbent articles include but arenot limited to diapers, adult incontinence briefs, training pants,diaper holders and liners, sanitary napkins and the like.

“Diaper” refers to an absorbent article generally worn by infants andincontinent persons about the lower torso.

“Disposable” is used herein to describe articles that are generally notintended to be laundered or otherwise restored or reused (i.e., they areintended to be discarded after a single use and, preferably, to berecycled, composted or otherwise disposed of in an environmentallycompatible manner).

“Comprise,” “comprising,” and “comprises” is an open ended term thatspecifies the presence of what follows e.g. a component but does notpreclude the presents of other features, elements, steps or componentsknown in the art, or disclosed herein.

The term “web material” refers to an essentially endless material in onedirection, i.e. the longitudinal extension, or the length, or thex-direction in Cartesian coordinates relative to the web material.Included in this term is an essentially unlimited sequence of pieces cutor otherwise separated from an essentially endless material. Often,though not necessarily, the web materials will have a thicknessdimension (i.e. the z-direction) which is significantly smaller than thelongitudinal extension (i.e. in x-direction). Typically, the width ofweb materials (the y-direction) will be significantly larger than thethickness, but less than the length. Often, though not necessarily, thethickness and the width of such materials is essentially constant alongthe length of the web. Without intending any limitation, such webmaterials may be cellulosic fiber materials, tissues, woven or non-wovenmaterials and the like. Typically, though not necessarily, web materialsare supplied in roll form, or on spools, or in a folded state in boxes.The individual deliveries may then be spliced together to form theessentially endless structure. A web material may be composed of severalweb materials, such as multilayer non-woven, coated tissues,non-woven/film laminates. Web materials may comprise other materials,such as added binding material, particles, hydrophilizing agents and thelike.

The terms “superabsorbent”, “super absorbent material” or “SAM”,“absorbent gelling material” or “AGM”, “absorbent polymer material” areused herein interchangingly, and refer to partially cross-linkedpolymeric materials, which can absorb water whilst they are swelling toform a gel.

All patents and patent applications (including any patents which issuethereon) assigned to the Procter & Gamble Company referred to herein,are hereby incorporated by reference to the extent that it is consistentherewith.

An exemplary absorbent structure is depicted in FIGS. 1 and 2. FIG. 1 isa plan view of a diaper 20 as a preferred embodiment of an absorbentarticle according to the present invention. The diaper is shown in itsflat out, uncontracted state (i.e., without elastic inducedcontraction). Portions of the structure are cut away to more clearlyshow the underlying structure of the diaper 20. The portion of thediaper 20 that contacts a wearer is facing the viewer. The chassis 22 ofthe diaper 20 in FIG. 1 comprises the main body of the diaper 20. Thechassis 22 comprises an outer covering including a liquid pervioustopsheet 24 and/or a liquid impervious backsheet 26. The chassis mayinclude a portion of an absorbent core 28 encased between the topsheet24 and the backsheet 26. The chassis may also include most or all of theabsorbent core 28 encased between the topsheet 24 and the backsheet 26.The chassis preferably further includes side panels 30, elasticized legcuffs 32, and elastic waist feature 34, the leg cuffs 32 and the elasticwaist feature each typically comprise elastic members 33. One endportion of the diaper 20 is configured as a first waist region 36 of thediaper 20. The opposite end portion is configured as a second waistregion 38 of the diaper 20. An intermediate portion of the diaper 20 isconfigured as a crotch region 37, which extends longitudinally betweenthe first and second waist regions 36 and 38. The waist regions 36 and38 may include elastic elements such that they gather about the waist ofthe wearer to provide improved fit and containment (elastic waistfeature 34). The crotch region 37 is that portion of the diaper 20which, when the diaper 20 is worn, is generally positioned between thewearer's legs. The diaper 20 is depicted with its longitudinal axis 100and its transverse axis 110. The periphery of the diaper 20 is definedby the outer edges of the diaper 20 in which the longitudinal edges 44run generally parallel to the longitudinal axis 100 of the diaper 20 andthe end edges 46 run between the longitudinal edges 44 generallyparallel to the transverse axis 110 of the diaper 20. The chassis alsocomprises a fastening system, which may include at least one fasteningmember 40 and at least one landing zone 42.

For unitary absorbent articles, the chassis 22 comprises the mainstructure of the diaper with other features added to form the compositediaper structure. While the topsheet 24, the backsheet 26, and theabsorbent core 28 may be assembled in a variety of well-knownconfigurations, preferred diaper configurations are described generallyin U.S. Pat. No. 5,554,145 entitled “Absorbent Article With MultipleZone Structural Elastic-Like Film Web Extensible Waist Feature” issuedto Roe et al. on Sep. 10, 1996; U.S. Pat. No. 5,569,234 entitled“Disposable Pull-On Pant” issued to Buell et al. on Oct. 29, 1996; andU.S. Pat. No. 6,004,306 entitled “Absorbent Article WithMulti-Directional Extensible Side Panels” issued to Robles et al. onDec. 21, 1999.

The topsheet 24 in FIGS. 1 and 2 may be fully or partially elasticizedor may be foreshortened to provide a void space between the topsheet 24and the absorbent core 28. Exemplary structures including elasticized orforeshortened topsheets are described in more detail in U.S. Pat. No.5,037,416 entitled “Disposable Absorbent Article Having ElasticallyExtensible Topsheet” issued to Allen et al. on Aug. 6, 1991; and U.S.Pat. No. 5,269,775 entitled “Trisection Topsheets for DisposableAbsorbent Articles and Disposable Absorbent Articles Having SuchTrisection Topsheets” issued to Freeland et al. on Dec. 14, 1993.

The absorbent core 28 in FIG. 1 generally is disposed between thetopsheet 24 and the backsheet 26. In addition to the absorbent sandwichstructure as described herein below, the absorbent core 28 may compriseany absorbent material that is generally compressible, conformable,non-irritating to the wearer's skin, and capable of absorbing andretaining liquids such as urine and other certain body exudates. Theabsorbent core 28 may comprise a wide variety of liquid-absorbentmaterials commonly used in disposable diapers and other absorbentarticles such as comminuted wood pulp, which is generally referred to asair felt. Examples of other suitable absorbent materials include crepedcellulose wadding; melt blown polymers, including co-form; chemicallystiffened, modified or cross-linked cellulosic fibers; tissue, includingtissue wraps and tissue laminates; absorbent foams; absorbent sponges;superabsorbent polymers; absorbent gelling materials; or any other knownabsorbent material or combinations of materials. The absorbent core 28may comprise a liquid storage region 60, and other liquid handlingelements 50, such as acquisition layers 52 and/or distribution layers54. The absorbent core 28 may further comprise minor amounts (typicallyless than 10%) of non-liquid absorbent materials, such as adhesives,waxes, oils and the like.

Exemplary absorbent structures for use as the absorbent assemblies aredescribed in U.S. Pat. No. 4,610,678 (Weisman et al.); U.S. Pat. No.4,834,735 (Alemany et al.); U.S. Pat. No. 4,888,231 (Angstadt); U.S.Pat. No. 5,260,345 (DesMarais et al.); U.S. Pat. No. 5,387,207 (Dyer etal.); U.S. Pat. No. 5,397,316 (LaVon et al.); and U.S. Pat. No.5,625,222 (DesMarais et al.).

The backsheet 26 may be joined with the topsheet 24. The backsheet 26prevents the exudates absorbed by the absorbent core 28 and containedwithin the article 20 from soiling other external articles that maycontact the diaper 20, such as bed sheets and undergarments. Inpreferred embodiments, the backsheet 26 is substantially impervious toliquids (e.g., urine) and comprises a laminate of a nonwoven and a thinplastic film such as a thermoplastic film having a thickness of about0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils). Suitable backsheetfilms include those manufactured by Tredegar Industries Inc. of TerreHaute, Ind. and sold under the trade names X15306, X10962, and X10964.Other suitable backsheet materials may include breathable materials thatpermit vapors to escape from the diaper 20 while still preventingexudates from passing through the backsheet 26. Exemplary breathablematerials may include materials such as woven webs, nonwoven webs,composite materials such as film-coated nonwoven webs, and microporousfilms such as manufactured by Mitsui Toatsu Co., of Japan under thedesignation ESPOIR NO and by EXXON Chemical Co., of Bay City, Tex.,under the designation EXXAIRE. Suitable breathable composite materialscomprising polymer blends are available from Clopay Corporation,Cincinnati, Ohio under the name HYTREL blend P18-3097. Such breathablecomposite materials are described in greater detail in PCT ApplicationNo. WO 95/16746, published on Jun. 22, 1995 in the name of E. I. DuPont.Other breathable backsheets including nonwoven webs and apertured formedfilms are described in U.S. Pat. No. 5,571,096 issued to Dobrin et al.on Nov. 5, 1996.

The diaper 20 may also include such other features as are known in theart including front and rear ear panels, waist cap features, elasticsand the like to provide better fit, containment and aestheticcharacteristics. Such additional features are well known in the art andare e.g. described in U.S. Pat. No. 3,860,003 and U.S. Pat. No.5,151,092. In order to keep the diaper 20 in place about the wearer,preferably at least a portion of the first waist region 36 is attachedby the fastening member 42 to at least a portion of the second waistregion 38, preferably to form leg opening(s) and an article waist. Whenfastened, the fastening system carries a tensile load around the articlewaist. The fastening system is designed to allow an article user to holdone element of the fastening system such as the fastening member 42, andconnect the first waist region 36 to the second waist region 38 in atleast two places. This is achieved through manipulation of bondstrengths between the fastening device elements. Diaper 20 according tothe present invention may be provided with a re-closable fasteningsystem or may alternatively be provided in the form of pant-typediapers.

The embodiments of absorbent structures according to the presentinvention comprise a laminate structure, generally also referred to as a“sandwich” structure. This refers to a design with two essentially flatouter layers, which are web materials or cut pieces of such webmaterials, as may be core web materials such as tissues, woven ornonwoven materials made from hydrophilized polymeric materials and thelike.

One preferred material is a so called SMS material, comprising aspunbonded, a melt-blown and a further spunbonded layer. Highlypreferred are permanently hydrophilic non-wovens, and in particularnonwovens with durably hydrophilic coatings. An alternative preferredmaterial comprises a SMMS-structure.

The top layer 56 and the bottom layer 58 may be provided from two ormore separate sheets of materials or they may be alternatively providedfrom a unitary sheet of material. Such a unitary sheet of material maybe wrapped around the storage layer 60 e.g. in a C-fold.

Preferred non-woven materials are provided from synthetic fibers, suchas PE, PET and most preferably PP. As the polymers used for nonwovenproduction are inherently hydrophobic, they are preferably coated withhydrophilic coatings. A preferred way to produce nonwovens with durablyhydrophilic coatings is via applying a hydrophilic monomer and a radicalpolymerization initiator onto the nonwoven, and conducting apolymerization activated via UV light resulting in monomer chemicallybound to the surface of the nonwoven as described in co-pending Europeanpatent application EP-A-1403419.

The storage layer 60 is positioned between the two layers of webmaterial and comprises a particulate material, in particular the abovementioned superabsorbent materials. Typically, these are in irregularlyshaped or spherical granules, which can swell upon contact with liquids,such as urine. Whilst this material may be in various shapes or forms,such as granular, spherical, flakes, fibrous, it will often consist ofirregularly shaped particles, having a mean particle size of from 10 μmto 1000 μm, preferably with less than 5% by weight having a particlesize of 5 μm, and preferably with less than 5% by weight having aparticle size of more than 1200 μm.

It has been found beneficial to use a particulate absorbent polymermaterial for absorbent cores made in the present invention. Withoutwishing to be bound by theory it is believed that such material, even inthe swollen state, i.e. when liquid has been absorbed, does notsubstantially obstruct the liquid flow throughout the material,especially when the permeability as expressed by the saline flowconductivity of the absorbent polymer material is greater than 10, 20,30 or 40 SFC-units, where 1 SFC unit is 1×10⁻⁷ (cm³×s)/g. Saline flowconductivity is a parameter well recognized in the art and is to bemeasured in accordance with the test disclosed in EP 752 892 B (Goldmanet al; P&G).

When employing such sandwich structures, there are a number of partlycontradicting requirements, which these structures have to satisfy foran acceptable performance.

Thus, the particulate material is preferably immobilized. This refers tomaintaining the arrangement of these particles in the structure duringproduction as well as during use. In modern articles, the absorbencyrequirements in different parts of the article can be very different,such that for example more absorbency and hence absorbent material maybe required in the proximity of the loading point than further away.Once the product design criteria have defined the absorbencydistribution profile, this should be produced and maintained throughoutthe use cycle of the article, and in particular during use.

Further, the particulate material should be enabled to swellunrestrictedly. Even modern absorbent material such as describedhereinabove exhibit absorbency properties depending to a certain extenton the pressure exerted on them. This pressure may be a regularuse-pressure, such as when the baby as a user sits on the article.However, such a pressure may be created in sandwich structures, when,for example, the outer web material layers 56 and 58 are tightly bondedto each other in a way which does not allow expansion, thusly reducingthe absorbency properties of the structure.

A further important requirement relates to the distribution of liquidthroughout the structure, both longitudinally (length wise orx-directionally) and laterally (cross- or y-directionally), but alsoalong the thickness or caliper (or z-direction) of the structure. Asdiscussed in the background section, it is known to arrange particles inan absorbent laminate or sandwich structure, with particulate absorbentmaterial arranged in particular pattern designs. The present inventionis aiming at producing a particular pattern under favorable productionconditions.

It has been found, that in particular for sandwich structures intendedfor liquid handling purposes, such for the use in absorbent structures,advantages for liquid handling properties can be realized, when thestructure is designed such that a cluster of particulate material is notfully separated from a neighboring cluster by a bonding line or region.An exemplary structure is exhibited in FIG. 3, showing a sandwichstructure 300 comprising a particulate material 310 sandwiched between acarrier material 320 and a cover material 330. Further, the particleclusters 350 are depicted as well as bonding point regions 360 andchannel regions 370 between neighboring clusters.

It further has now been found, that it is of particular benefit thatbetween adjacent clusters there is a bonding zone, which is essentiallyfree of any particles, thusly allowing a good bond between the carrierlayers, such as through gluing, or other means.

Nonetheless, the structure should enable good immobilization or theabsorbent particles, in particular when these are wetted. In particular,the absorbent structures or the absorbent article comprising suchstructures should provide more than 50% preferably more than 60%, evenmore preferably more than 80% and most preferably more than 90% whentested in the Wet Immobilization Test, such as described in EP1447066(Busam et al.; P&G).

A pattern of particulate material is considered to comprise a pluralityof particle clusters 350, each comprising a plurality of particles 310.

Such a particle cluster (refer to FIGS. 3A and B) may comprise as few asabout 10 particles, but may also be up to several hundred or evenseveral thousands of particles. The particles may be arrangedessentially in a “monolayer” sandwich structure, or multi-layerstructures of essentially constant thickness, or may have varyingthickness. This thickness may be expressed in terms of number ofoverlaying particle layers, or may be expressed by a local or anaveraged basis weight, referring to the weight of particles for a givenunit area. The skilled person will readily realize, that even a “local”basis weight will need a certain amount of averaging. However, when thebasis weight in a given region is by design not constant over thisregion, such as may be with an increase towards the centre of the regionin case of a heap or pile of granular material, the basis weightdistribution may be approximated by a smoothed curve when following across-sectional view through this heap. Alternatively, the basis weightof a region may be designed to be constant throughout the region, suchthat an average basis weight for this region can be determined,optionally together with certain variability thereof. The basis weightof the neighboring regions can be the same, but is not required to beso. Typical basis weights as averaged over a particle cluster range from10 g/m² or even less to 500 g/m² or even 1000 g/m². Typical basisweights averaged over a pattern (i.e. including both particle clusterand the regions between these clusters, which can be essentially free ofparticles) range from 1 g/m² to more than 400 g/m² or even more than 800g/m².

A cluster 350 may have various forms and shapes, such as oval orelliptic or may be irregularly shaped. In a preferred embodiment theseclusters are essentially circular. A cluster may have a diameter 353 ofmore than 2 mm, preferably more than 4 mm, but less than 20 mm,preferably less than 8 mm. The distance 355 between two neighboringclusters in a pattern 380 may be more than 2 mm, preferably more than 5mm, but less than 30 mm, preferably less than 15 mm, and even morepreferably less than 7 mm.

A plurality of clusters is forming a primary pattern wherein theclusters are spaced apart in any geometric way. Such a pattern maycomprise as few as two clusters, but will typically comprise more thanten clusters. Often, it will comprise less than 1000 clusters. Anyplurality of cluster may form regular or irregular sub-patterns of theprimary pattern. The clusters may be discrete or disconnected regions,such that each of these regions is essentially circumscribed by a regionwhich is essentially free of particles. These particle free regions donot need to be identical to the bonding regions.

Typically, the particles are arranged to be in direct contact to eachother, i.e. each particle will be in contact with at least one otherparticle. It may, however, also be the case, that they do not contacteach other. Then however, the distance between neighboring particleswithin a cluster will generally be less than the distance of neighboringparticle clusters within the primary or sub-pattern.

Whilst the patterns are formed in an essentially continuous arrangement,there will be a certain repetition of the pattern, which will allow thesame pattern to repeat in subsequent articles. Thus, the term“macro-pattern” refers to such a repeating pattern each of which mayform an element of such an article.

Any of these discrete regions may be arranged in a macro pattern, suchas being formed by at least two discrete regions forming a repeatingpattern with varying, and generally larger continuous regions therebetween.

A pattern may be described by a characteristic axis, such as indicatedby axis 383 in FIG. 3. Preferably, this axis is angularly offset to thelongitudinal axis 100 of the diaper 20 or of the absorbent corerespectively.

The bonding regions 360 between the clusters are preferably distinctregions rather than continuous regions, which would prevent channelregions 370 to be formed between the clusters. The bonding points mayhave varying shape and dimensions. In a preferred embodiment, thebonding regions 360 have a circular form of a diameter 363 of not lessthan about 1 mm, preferably not less than 2 mm, or even not less thanabout 5 mm. Further, the bonding point region diameter is preferablyless than about 20 mm, preferably less than about 10 mm. The distance365 of adjacent bonding points is primarily defined by the clusterpattern and may be not less than about 5 mm, preferably not less thanabout 10 mm, but less than about 20 mm, preferably less than about 15mm. A pattern can be unitary or can consist of sub-patterns; each ofthese sub-patterns may have different dimension or distances,respectively. The transition between sub-patterns may also be a gradualone. A pattern should be repeatable for subsequent absorbent structuresfor, e.g., a diaper.

In addition to the bonding regions 360, there may be a peripheralbonding 387, so as to seal the sandwich structure at the longitudinal orend edges.

Process for Producing Patterned Sandwich Structures

In a particular aspect, the present invention relates to a method ofproducing a sandwich structure having a pattern of particulate materialenveloped between a carrier material.

Such a process should allow a very precise and repeatable production ofthe pattern at high or very high production speeds, i.e. preferably notbeing the overall speed production limiting process step in the overallproduction process, which may be up to 0.5 m/sec but often are 10 m/secor even higher. Even further, the process should enable robust andinexpensive equipment designs.

Thus, the present invention relates to an essentially continuouslyoperated lay-down of particulate material onto a surface, which ismoveable at a preset surface speed, in a predetermined pattern. Thepattern consists generally of regions comprising particulate material,and regions being essentially free of particulate material.

A schematic representation of the process can be seen in FIG. 4, showinga particulate material supply 410, supplies 420 and 430 for carriermaterial 320 and cover material 330 respectively, a carrier supportmeans 470, and the optional element of a particle transfer devices 440.Also shown is the resulting sandwich structure 300 with the particulatematerial 310 between carrier material 320 and cover material 330.

The particulate material is generally supplied to the process from aparticle storage system, and generally will be supplied in bulk form.Bulk refers to the fact, that the multitude of particles may bedescribed by properties and parameters relating to an individualparticle, such as composition, size, shape, particle density, and so on,but also by properties and parameters relating to a multitude of suchparticles, such as bulk density, particle size distribution, or flowproperties.

The particulate material is deposited on a moving surface of a webmaterial. Thusly, the process may exemplary be described to positionparticles from a bulk storage system in a regular pattern onto a webmaterial.

Such processes require not only an accurate positioning of theparticulate material, but should be compatible with high of even veryhigh “converting” speeds, which correspond within the current contextgenerally to the speed of the moving surface.

Many current particle deposition systems as described in the backgroundsection hereinabove are generally very speed dependent, and eithercreate unacceptable losses or variability with regard to positioning andapplied weights when being run at such speeds. Co-pending EP-Patentapplication, which is incorporated herein by reference provides asolution for the aforementioned difficulties by providing a method forindirectly applying absorbent gelling material granules onto a carrierlayer for use in an absorbent article, particularly a diaper, whereinparticulate granules are taken up by a transfer device from a bulkstorage. Referring to FIG. 4, the transfer device 440 has recesses 452on the surface, wherein the number, size and position thereof determinethe amount and pattern of superabsorbent particles 310 taken up by thetransfer device 440. The transfer device 440 is moveable from a loadingposition 442 adjacent to the bulk storage 410 to a discharging position448 at which the carrier layer 320 is adjacent to the transfer device.The transfer device further has a means 444 for retaining thesuperabsorbent particles inside its recesses during movement of thetransfer device 440 to the discharging position 448, and a means 446 forexpelling the particles onto the carrier layer at the dischargingmeeting position 448. Preferably, these means are vacuum and blow offair, respectively.

The present invention provides a method for creating a pattern of aparticulate material sandwiched between a carrier material by depositinga pre-metered amount of the particulate material 310 on a carrier web320, which forms a particular pattern of indentations 328, i.e. which isdeformed out of the flat plane. This is achieved by placing the carriermaterial 320 on a carrier support structure 470 forming a particularpattern. Between the structure elements 475 forming this pattern thereis essentially free space allowing the carrier web to bulge into thisspace upon drawing forces, such as may be accomplished by a vacuumsuction 472 generating a gas (air) flow through the fluid or airpermeable carrier material 320. The particulate material 310 is thenpositioned in these indentations, thusly forming a cluster 350, and mayfill these indentations partly, completely or may over-fill these, suchas by forming a “heap”. In any of these cases, at least a part of thecarrier material is essentially free of particulate material. This areais referred to as the bonding region 360, which may correspond to thecarrier support area 322, or which may be larger or smaller than this.

The formation of the sandwich structure is completed by covering thepatterned particulate material of the indentations 350 with a covermaterial 330 and fixing the two web materials to each other, such as byapplying adhesive material 495 at least to the bonding region of thecarrier material or to the corresponding area of the cover material.According to the present invention, the carrier material 320 ispositioned onto a carrier support means 470. The carrier support means470 comprises a surface, which may be brought into contact with thecarrier material at a matched speed. Such a match is achieved, if thesurface moves with a speed which corresponds to the overall processspeed.

The carrier support means may be of cylindrical shape rotatablypositioned around its longitudinal axis. The outer cylindrical surfacesuch as the shell 450 of a rotating drum will then form the supportregion for the carrier material. The carrier support means may alsocomprise an essentially endless moveable belt carried upon a system oftransporting rollers.

The carrier material 320 will be positioned on the “outer” surface ofthe carrier support means, outwardly referring to the outer surface of adrum, or to the surface opposite to that surface of a moving belt, whichis in contact with the majority of the belt support rollers.

The carrier web will be positioned onto the carrier support area 477.This sub-region of the carrier support means is the area, which is incontact with the carrier web, when this is positioned in an essentiallyuntensioned state onto the carrier. Thus, if the carrier support meanswere a continuous (unapertured) drum, the carrier support area would bethe cylindrical surface. It the carrier support means were an apertureddrum, the carrier support area would be the area of the cylindricalsurface minus the area of the apertures. If the carrier support meanswere a square grid formed into a cylindrical shape, the carrier supportarea were the outwardly facing areas of the ribs of the grid.

In a preferred embodiment, the carrier support area is not a continuousregion, i.e. the carrier support area can be represented by “islands”,such as may be created by pins 475 protruding of the cylinder shell 450(FIG. 5). The outermost surface covering the outward end points of thepins 475 corresponds to the carrier support area 477. The support pinsmay have a rectangular cross-section. In a preferred embodiment, thesupport pins have a cylindrical shape, having a diameter 376 ofpreferably more than 1.5 mm, more preferably of more than 5 mm, but notmore than 15 mm, more preferably of not more than 10 mm. If theoutermost surface of the pins is not a flat surface (see FIG. 6A, B),but for example has a rounded, oval or circular cross-sectional shape(see FIG. 6C, D), the area referred to is the projection to the area aswould be covered by the carrier web support material in an essentiallyuntensioned state. The carrier support area may also be formed byridges, which may be straight or curved, or in the form of a cross (seeFIG. 6E, F). The carrier support area may be formed by “hybrid”structures, such as pins protruding out of a grid or a cross, or a gridhaving varying heights, such that, for example the intersections pointsof the grip form the most outward oriented areas (see FIG. 6G, H).

Thus, the carrier web means is intended to be supported by the (mostoutwardly) oriented carrier support area, but it may bulge or deformradially inwardly in the area other than the carrier support area bymechanisms as described herein below.

However, for certain designs, it may be appropriate to support thecarrier material not only at the outer enveloping surface, but to alsosupport the carrier material in a secondary support area. Such an areacan be compared with “low level islands”, which do not have contact withthe carrier material if applied without deforming forces, but which willcontact this only upon a certain deformation (inward bulging) of theweb, and then support it. For example, there can be one set on carriersupport pins having a certain height so as to form the primary carriersupport area, and a second set of pins having a lower height so as toform the secondary support area (see also FIG. 6G, H).

The carrier support area will form a particular, predefined pattern.This pattern corresponds to the desired particulate material pattern inthe sandwich structure. Preferably, it has a macro pattern generallyalong the x-direction of the web running over the carrier web supportmeans, but arranged at a predefined angle (see FIG. 5C). This may berepeating, and will typically reflect the pattern of the patternedabsorbent sandwich structure.

The dimensions of the carrier support area should further be adapted tothe overall properties of the carrier material. For example, when usingsupport pins, the support area of an individual pin should not be belowa critical area, under which the local stress in the web might causedestructive deformation, or penetration of the pin through the pores ofthe web.

These pins may be positioned at distances to the next neighboring pin of5 mm or the distance may be 20 mm or more. These pins may have acylindrical shape. In order to avoid damaging of the supported webmaterial, each individual pin should have an essentially outwardlyfacing surface of at least 3.5 mm², preferably 10 mm², but not more than40 mm². The pins may also have a non-cylindrical shape at the outwardlyfacing tip, which is in contact with the web. The contacting area willthen be considered to be the projection of the part of the tip being incontact with the carrier material upon deformation to a plane as formedby the carrier material in an untensioned state. Alternatively or inaddition, the carrier support pattern may also be in the form of anothergeometrical pattern, such as by elongated pins, or ribs or ridges, whichmay be straight or curved. Preferably, these do not form a continuouspattern; however two or more ribs may be connected, for example forminga cross-shaped support area. The carrier material has to satisfy therequirements for the final resulting structure, such as liquid handlingproperties in the case of fluid handling applications.

Further, the carrier material has to have the ability to deform underforces as applied during the process. Whist these forces can by ofvarious types, the most preferred one is the drag force resulting fromapplying a fluid flow through a fluid permeable carrier material. In aparticularly preferred embodiment, the carrier material is airpermeable, such by being an apertured film material or even morepreferable a fibrous web.

The air permeability is connected to the material pore size andthickness, and hence—in the case of fibrous materials—to the intrinsicdensity of the fiber material and the diameter of the fibers,respectively the diameter distribution in case of fibers having varyingdiameter. Further the carrier material has to have the ability to retainparticles as deposited thereon.

This may be related to the permeability of the carrier material, as theabove mentioned pore size may allow small particles to pass through.Whilst this is not desired in principle, a certain amount of “fines” canbe accepted to pass through. This may be then be recovered downstream.

Important for the present invention are the deformation properties ofthe carrier material. Deformation refers to the ability to elastically(i.e. essentially recoverably) or plastically deform upon application offorces as exerted by the carrier web deformation and fixation means.

As the most carrier materials for the present invention will beessentially two-dimensional webs having an machine, longitudinal, orx-directional extension and a cross-machine, transversal, ory-directional extension perpendicular to the first.

Upon application of a force in any directions, the material willelongate along this direction. Thereby, the material will tend tocompensate for this elongation by reducing its flat dimensionperpendicularly to the direction of the direction of the force, as wellas its thickness along the z-direction. Typically, web materials aredescribed by their properties measured along the machine direction (MD)as well as in cross-direction (CD), such by creating stress-strainprofiles and/or defining certain characteristic points of theseprofiles. Typically, such properties are determined by clamping a stripeof the material and applying pull forces to the clamp. The carriermaterial can further be characterized by its mechanical properties,namely its CD- and MD-extensibility at certain loads, such as may bedetermined by conventional stress-strain measurements using line clampsat a crosshead speed of 0.127 m/min. Preferably, the ratio of CD to MDelongation is more than 1 to 0.2, but preferably not more than 1 to 2.

As will be described herein below, useful carrier materials will besubmitted to a force as may be generated by a fluid flow through thematerials, such that a force in z-direction will be applied. However, asthe carrier material is supported in the carrier support area, such asby carrier support pins, the deformation in this case will be determinedby the CD- and MD-deformation properties. Henceforth, these propertieshave to be adjusted to the support area pattern.

The carrier material will be temporarily affixed to the carrier supportmeans and will be deformed out of its flat/plane arrangement by thematerial holding means. Whilst a multitude of physical principles may beused, such as magnetic forces in case of magnetically respondingmaterials, a particularly preferred embodiment relies on the use offluid flow through the web.

To this end, the carrier support means may comprise a vacuum suctionmeans 472, arranged such that gas—in particular air—is drawn through theweb material. Based on the flow resistance due to the porosity of theweb, the flow will induce a force in the z-direction, and thus deformthe unsupported parts of the web.

Consequently, the web will form an indentation 328 (see FIG. 4B), theupper points will be defined by the support area (e.g. the supportpins), and the “bottom of the valley” will be defined by the ratio ofvacuum suction force, permeability and stress-strain properties of thecarrier material. Thus, if an essentially homogeneous material wouldhave the same properties in MD- and CD-direction, and—for example—theweb support structure would consist of support pins arranged in aquadratic arrangement, the indentation would form a trough with itsdeepest points in the centre of the square.

Defining a space curve to connect two points of the squarely arrangedsupport pins to follow the deformation of the web material willgenerally result in longer curve lengths than the linear distance ofthese support pins, and if the curve connects two diagonally opposedpoints, the space curve will have the longest length, generallyfollowing a shape which can be approximated by a hyperbolic curve.

Similarly defining an outer surface by connecting the support area—i.e.in the present case the square connecting the four corner points of thesupport pins, and thus the area of the web covers before applying thesuction forces—this can be compared to the actual surface area of thedeformed material forming the indentation.

Similarly, a volume can be defined for the indentation formed by thedeformed carrier material, which is circumscribed by the deformed webmaterial and the surface as covered by the web material prior todeformation through the deformation means. Preferably, this volume is atleast 30 mm³, preferably at least 100 mm³, but less than 1000 mm³.

This “indentation volume” can be compared to the volume of theparticles, which are to be positioned therein. Depending on the designtarget, the volume of the particles of a cluster may fill more than 5%of the volume of the indentation, or more than 50% of the volume. In thecase of “overfilling” (or forming a heap), the indentations willtypically not be filled by more than 150% of their volume.

After the carrier material 320 has been deformed to form theindentations 328 and the particulate material 310 has been positioned inor on these indentations, the structure is covered by a cover material,typically a web material, too. This cover material is primarily definedby the requirements of the final application. It may be the samematerial as the carrier material, and may be unitary with the carriermaterial, such as when then particulate material is deposited in aregion—such as the centre stripe region—of a web material and laterallyoutwardly oriented part or parts of the material are then folded oversuch as along a longitudinal fold line, so as to cover the particulatematerial.

It may also be the same kind on material, but being supplied separately,or it may also be a different material, which is suitable for theintended application as well as for being bonded to the carriermaterial.

The carrier material and the cover material are connected to each other,such as permanently bonded so as to form the composite sandwichstructure with the particle pattern between. This bonding can beachieved by conventional means, such as adhesives, or thermo bonding orthe like.

It has been found important, that the bonding is not impeded byparticles positioned between the webs in the bonding regions. Bondingregions refers to regions, which are essential for ensuring goodpermanent bonding. Thus, in the above described example of support pinsforming the support area, the bonding region will generally coincidewith this area, but may be somewhat smaller or larger than the supportarea.

For example, when spray applying adhesives, it might be preferable tohave a bonding area of more than 2%, preferably of more than 7%, butless than 50% of the total pattern area. The bonding area may be largerthan the support area, which will typically be the case when theindentations are not completely filled with particulate material. Ifapplying melt fusion bonding at the support pins, the bonding area mightbe as little as 50% of the support area.

Thus, the bonding region is preferably essentially free of particulatematerial. The term “essentially free” refers to the fact that anyparticles present in this area should not lead to break up of thebonding under normal use conditions.

However, if the particulate material exhibits a broad particle sizedistribution profile, or if particle break up is created during theprocess, a certain amount of “dust” is acceptable in this regions. Amethod of assessing the amount of “bonding region particle loading” isdescribed hereinafter for the application of absorbent materials.

After having described the elements required for executing the presentinvention, the following will describe the individual process steps.

Overall, it is assumed, that a sandwich structure is to be producedcomprising particulate material in a predefined pattern. The process isan essentially continuous process, starting from essentially endless webmaterials and combining these with particulate materials as provided inbulk supply form. The resulting continuous sandwich composite may beseparated, such as by cutting, into individual pieces, each comprisingat least a macro pattern of the particulate material sandwich.

The individual process steps are now explained in more detail. The orderdoes not necessarily reflect a chronological order for these steps.

-   -   a—An essentially flat web material is provided to serve as        carrier material and/or as cover material forming the outer        sandwich layers. Thus, the web material may be unitary forming        both outer sandwich layers such as by longitudinal folding.        There may also be two different web materials, one forming the        carrier material, and the other the cover material. In a        preferred execution, the web materials are separate, but of the        same type. The properties of the web materials have to be        compatible with the indented use. In addition and in a preferred        embodiment, the carrier material is permeable for gas, such as        air, but not for particles. In a preferred embodiment, the web        materials are nonwoven materials, and more preferably a        combination of a spunbonded layer (S) with a meltblown layer, so        as to form a SMS or more preferably a SMMS type web.    -   b—An essentially endless support means for the carrier having a        support pattern is provided, preferably a rotatable drum with        the support pattern being on the outer cylinder or shell surface        of this drum. Preferably, the carrier support pattern is formed        by carrier support pins. Such pins extend towards the outer        surface of the carrier support means, which then can generally        be described by enveloping the outwardly facing areas of theses        pins.    -   c—In order to first hold the carrier material and to then form        indentations therein, a carrier material holding means is        actuated. In the preferred embodiment of the carrier means being        a rotating drum respectively the rotating shell of a drum, and        the carrier material is a an air permeable material which is        positioned on this shell, the carrier material holding means may        be vacuum suction inside the drum. This may be achieved by        non-rotating vacuum boxes underneath the surface of the drum.        Thereby, air is sucked through the carrier material in this        section, thereby exerting forces on the web, thusly holding it        affixed on the surface of the drum and deforming it in        unsupported regions. The amount of suction, i.e. the degree of        vacuum created depends on the permeability properties of the        web, the unsupported area, and the desired deformation (i.e. the        size of the indentations).    -   d—The carrier material is guided towards the outer surface of        the carrier web support and deformation means at a match speed,        e.g. the carrier material moves at a carrier speed of more than        0.5 m/sec, more preferably more than 5 m/sec, matching the        radial outer surface speed of the carrier support drum.    -   e—As a further process step, a particulate material is provided,        such as conventional superabsorbent particles. Preferably this        material is provided in bulk form, such as in a hopper.    -   f—This material is metered and dosed according to the        requirements in the resulting product. This dosing may be        constant over time or variable. In a preferred embodiment, the        dosing already pre-forms a particle cluster in a particular        pattern, as may be desirable for the resulting product.    -   g—The particulate material is then transferred to the outwardly        facing surface of the carrier material, or the receiving surface        of the carrier material, while this is supported by in the web        support areas on the web support means, and deformed in to        indentations in the unsupported regions.    -   h—Further, a sandwich fixation means is actuated for affixing        the carrier material and the cover material while the particle        pattern is maintained. In a preferred embodiment, the fixations        means is application of spray glue before and/or after the        particles are transferred onto the carrier material. In case of        carrier and cover web having matching melt properties, the        bonding means may also be heat fusion bonding, such as by        ultra-sound. The carrier and cover webs are affixed to each        other in the bonding area. The bonding area can be described by        at least covering the web support area, but will typically        extend longitudinally and laterally outwardly of this region,        thusly covering an area of more than 2%, preferably of more than        7%, but less than 50% of the support region. Preferably, the        bonding area is preferably essentially free of particles. This        requirement can be assessed by using the method for determining        particles in the bonding area, as described in the method        section herein below. Optionally, the bonding means may also be        applied to the particles.    -   i—After the particles are positioned on the carrier material the        cover material is applied and bonded to the carrier material,        thereby closing the sandwich structure. This is a preferred but        optional step. In accordance with the present invention a        sandwich structure comprising a carrier material but no cover        material can be provided, as the sandwich fixation means can        provide sufficient integrity to the structure and make it a        sandwich-like structure, such that it is unnecessary to further        provide a cover material.

During this process, it is important, that the carrier web is supportedonly in the support pattern region of the web support means, and thatthe carrier material is deformed by the carrier holding means such thatindentations are formed in the unsupported regions. This forms a primarypattern, optionally comprising sub-patterns. The pre-metered particulatematerial is preferably deposited essentially exclusively in theseindentations, preferably thereby filling at least 5% of the indentationvolume, preferably filling not more than 150% of the indentation volume.

Method for Determining Absence of Particles in Area

The test has the purpose of assessing the bonding areas with regard tocontamination of particulate material, in particular of superabsorbentmaterial.

A test solution is prepared by diluting 1.5 g of purple bromocresolindicator (CAS number 115-40-2) in 10 l of de-ionized water, and adding4 ml of 1 mol/l hydrochloric acid (1 N HCl). The test specimen is wettedby the test solution, e.g. by using a pointed pipette and adding thesolution drop wise, or by using a fine spray bottle. The amount of addedtest liquid will depend on the size of the sample and the amount ofsuperabsorbent material. It should be sufficient to wet all particles inthe considered region so as to ease visual counting, which is thenperformed on the respective regions. The assessment may also besupported by employing a magnifying glass or a microscope with suitablemagnification. Very fine particles also referred to as dusts, andgenerally having a size corresponding to the pore size of the carrierand/or cover material, are not counted.

A region is classified as being “free of superabsorbent particles”, ifless than two particles are detectable. A region is classified as being“essentially free of superabsorbent particles”, if particles present inthe bonding area do cover more than about 50% of this area.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this written document conflicts with any meaningor definition of the term in a document incorporated by reference, themeaning or definition assigned to the term in this written documentshall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

Each parameter for which a value is defined herein is a technicalparameter, which in the context of the present invention is not to beunderstood literal. Hence, all embodiments having parametersfunctionally equivalent to the parameters stated herein are intended tobe covered by the scope of the invention, e.g. a length of “10 mm” hasto be understood as meaning “about 10 mm”.

1. A method for producing a sandwich structure comprising a pattern ofparticulate material, said method comprising the steps of: a.) providingan air permeable carrier material and a cover material, wherein each ofthe carrier and cover material include at least one essentially flat webmaterial; b.) providing an essentially endless support means for saidcarrier material having a support pattern, said support patterncomprising a plurality of support pins on the outer surface of thesupport means, said support pins having an outwardly extending surfaceof at least about 0.8 mm²; c.) providing a carrier material holdingmeans comprising vacuum air suction; d.) positioning said carriermaterial over said essentially endless support means, whereby saidcarrier material contacts only said support pattern with its supportsurface and whereby the relative speed between carrier material and thecontact surface of said carrier support means is essentially zero; e.)providing a particulate material; f.) pre-metering the amount of theparticulate material; g.) transferring the particulate material to thecarrier material and providing a sandwich fixation means; h.) combiningsaid cover material with said carrier material and said particulatematerial being sandwiched there between; i.) supporting said carriermaterial only in the region of the support pattern of the support means;j.) deforming said carrier material by said carrier material holdingmeans such that indentations are formed in the unsupported regions ofsaid carrier material; and k.) transferring said particulate materialinto said indentations of said carrier material, thereby forming aprimary pattern of particulate material.
 2. A method for producing asandwich structure according to claim 1, wherein said carrier materialis a non-woven material selected from the group consisting of SMS typeand SMMS type.
 3. A method for producing a sandwich structure accordingto claim 1, wherein said carrier material has a CD-extensibility or aMD-extensibility of more than about 20%.
 4. A method for producing asandwich structure according to claim 1, wherein said carrier materialhas a ratio of MD-extensibility to CD-extensibility at a given load ofnot more than one to two.
 5. A method for producing a sandwich structureaccording to claim 1, wherein said cover material is a non-wovenmaterial.
 6. A method for producing a sandwich structure according toclaim 1, wherein said particulate material is a bulk material.
 7. Amethod for producing a sandwich structure according to claim 1, whereinsaid carrier support means is a rotatable drum, preferably having anouter cylinder shell.
 8. A method for producing a sandwich structureaccording to claim 1, wherein said carrier support pins have a distanceof more than 5 mm from each neighboring support pin.
 9. A method forproducing a sandwich structure according to claim 8, wherein saidcarrier support pins have a distance of not more than 30 mm from eachneighboring support pin.
 10. A method for producing a sandwich structureaccording to claim 1, wherein said carrier material has a support regionand a bonding region that is at least 2% of the support region.
 11. Amethod for producing a sandwich structure according to claim 10, whereinsaid bonding region is not more than 50% of the area of the pattern areasupport region.
 12. A method for producing a sandwich structureaccording to claim 1, wherein said bonding region comprises essentiallyno particulate material, as assessed by the method for determining theabsence of particles in the bonding area.
 13. A method for producing asandwich structure according to claim 1, wherein said carrier fixationmaterial holding means extends said carrier material such that saidcarrier material deforms out of the original flat state forming anindentation.
 14. A method for producing a sandwich structure accordingto claim 13, wherein said indentations have a volume of more than 30mm³.
 15. A method for producing a sandwich structure according to claim13, wherein the particulate material fills more than 5% of the volume ofsaid indentations.
 16. A method for producing a sandwich structureaccording to claim 15, wherein the particulate material fills not morethan 150% of the volume of said indentations.